Using an IP address both for routing address and session identification is a cause for problems encountered in mobility, multi-homing (multiple IP addresses), security etc. Separation of session identifier and routing address addresses some of these problems. However, the concept of what to anchor in the network (whether an IP address or a session or flow) remains problematic. Existing mobility systems employing anchors have been anchoring without distinguishing between IP address and session/flow, so that they are anchored together. The failure to distinguish and to separate them makes it difficult if not impossible to change or move the anchors.
Examples of the current use of anchoring are as follows. (1) In Mobile IP, the home agent is the anchor, which is at the link that allocates and advertises routes for the IP address (home address HoA). The home agent cannot change. (2) In Proxy Mobile IP, the Local Mobility Anchor (LMA), which is at the link that allocates and advertises routes for the IP address (home address HoA). Again it is difficult if not impossible to move or change the Local Mobility Anchor. (3) In 3GPP EPC network, the anchor of a PDN connection is the P-GW, which allocates and advertises routes for the IP address. Change of P-GW is currently impossible. (4) In 3GPP UMTS network, the GGSN is the anchor, which allocates and advertises routes for the IP address.